1. Field of the Invention
The present invention relates to a telephone subscriber station having a base set connected to the telephone network and a cordless hand set, with a first transmission path which contains a first low frequency/pulse phase modulation (NF/PPM) converter and a first infrared (IR) pulse transmitter in the base set and, connected by way of a first optical transmission channel, comprises a first IR pulse receiver and a first pulse phase modulation/low frequency (PPM/NF) converter in the cordless hand set, and a second transmission path which comprises a second NF/PPM converter and a second IR pulse transmitter in the cordless hand set and, connected by way of a second optical transmission channel, includes a second IR pulse receiver and a second PPM/NF converter in the base set, and which includes a delay circuit for phase synchronization in the base set and a dial and/or calling device in the hand set.
2. Description of the Prior Art
Such a telephone subscriber station is generally disclosed in the German published application No. 2,823,931 and its operation is described below on the basis of FIGS. 1 and 2, on which FIG. 1 is a block diagram of a telephone subscriber station according to the aforementioned German application and FIG. 2 is a pulse diagram for pulse phase modulation for such a station.
The abbreviations employed herein have the following meanings:
PPM=pulse phase modulation; PA1 NF=audio (low) frequency; PA1 MFV=multifrequency method; PA1 IWV=pulse selection method; PA1 IR=infrared; PA1 MFS=multifrequency signal in the transmission section; and PA1 MFE=multifrequency signal in the receiving section.
The block diagram of FIG. 1 illustrates a base set 1 and a cordless hand set 2.
The base set 1 comprises an IR pulse transmitter 4, an IR pulse receiver 8, a PPM/NF converter 19, a NF/PPM converter 20, a sawtooth generator 21, a delay circuit 22 and optionally, a telephone set 15 having a cord and a dialing device, as well as a power supply 24.
The cordless hand set 2 comprises an IR pulse transmitter 7, an IR pulse receiver 5, a NF/PPM converter 25, a PPM/NF converter 26, a sawtooth generator 27, a microphone 28, a receiver ear piece 29, a call or dialing device 30 and a power supply 31.
When a speech signal appears on the leads 23 of the subscriber line, the speech signal is converted into PPM signals in the NF/PPM converter 20 and is transmitted into the optical transmission channel 3 by way of the IR pulse transmitter 4. This signal is received by the IR pulse receiver 5 and is fed to the receiver ear piece 29 by way of the PPM/NF converter 26. A reply returns to the leads 23 of the subscriber line by way of the microphone 28, the NF/PPM converter 25, the IR pulse transmitter 7, the optical transmission channel 6, the IR pulse receiver 8 and the PPM/NF converter 19.
A dialing device can be located in the base set 1 and/or in the cordless hand set 2. The arrangement 30 and the cordless hand set 2 can be either a call or a dial device. If this is only a matter of a call device, then the selection of a called party must be carried out by a person at the base set. If the arrangement 30, however, is a dialing device, then the called party can be directly selected.
The NF/PPM converter 25 and the PPM/NF converter 26 are driven from a common sawtooth generator 27 and the NF/PPM converter 20 and the PPM/NF converter 19 are driven by a common sawtooth generator 21. The synchronization of the sawtooth generator 21 with the sawtooth generator 27 occurs by way of a delay circuit 22, preferably a phase locked loop.
FIG. 2 illustrates a pulse diagram for the PPM transmission between the hand set and the base set.
The sawtooth wave c is generated by a free-running sawtooth generator 27 of the hand set; whereas the sawtooth wave g is generated by the sawtooth generator of the base set. A sawtooth period of, for example, 125 .mu.s, is divided into two channels K1 and K2. PPM pulses are transmitted in the channel K1 from the hand set to the base set, while PPM pulses are transmitted in the channel K2 from the base set to the hand set. A PPM pulse a is emitted by the IR pulse transmitter 7 of the hand set and is received, now referenced d, by the IR pulse receiver 8 of the base set. The PPM pulse e is transmitted by the IR pulse transmitter 4 of the base set and, referenced b at the receiving side, is received by the IR pulse receiver 5 of the hand set. The swing of the PPM pulses amounts to approximately .+-.30 .mu.s.
Dial signals are transmitted from the hand set to the base set in a variation of a pulse dial method. This requires considerable circuit expense and is unsuitable for permutation code switching.